This invention relates generally to automatic test equipment. More particularly, this invention relates to a device for mechanically attaching automatic test equipment with machinery that positions semiconductor devices for testing.
Semiconductor manufacturers generally test semiconductor devices at various stages of production. During manufacturing, integrated circuits are fabricated in large quantities on a single silicon wafer. The wafer is cut into individual integrated circuits called dies. Each die is loaded into a frame, and bonding wires are attached to connect the die to leads that extend from the frame. The loaded frame is then encapsulated in plastic or another packaging material to produce a finished product.
Manufacturers have a strong economic incentive to detect and discard faulty components as early as possible in the manufacturing process. Accordingly, many semiconductor manufacturers test integrated circuits at the wafer level, before a wafer is cut into dies. Defective circuits are marked and generally discarded prior to packaging, thus saving the cost of packaging defective dies. As a final check, many manufacturers test each finished product before it is shipped.
To rapidly test large quantities of semiconductor components, manufacturers commonly use automatic test equipment (xe2x80x9cATExe2x80x9d or xe2x80x9ctestersxe2x80x9d). In response to instructions in a test program, a tester automatically generates input signals to be applied to an integrated circuit, and monitors output signals. The tester compares the output signals with expected responses to determine whether the device under test, or xe2x80x9cDUT,xe2x80x9d is defective. Because testers are highly automated, they can run millions of tests in only a few seconds.
Customarily, component testers are designed in two different portions. A first portion, called a xe2x80x9ctest head,xe2x80x9d includes circuitry that is preferably located close to the DUT, for example, driving circuitry, receiving circuitry, and other circuitry for which short electrical paths are essential. A second portion, called a xe2x80x9ctester body,xe2x80x9d is connected to the test head via cables, and contains electronics that are not required to be close to the DUT.
Special machines move and electrically connect devices to a tester in rapid succession. A xe2x80x9cproberxe2x80x9d is used to move devices at the semiconductor wafer level. A xe2x80x9chandlerxe2x80x9d is used to move devices at the packaged device level. Probers, handlers, and other devices for positioning a DUT relative to a tester are generically known as xe2x80x9cperipherals.xe2x80x9d Peripherals generally include a site where DUTs are positioned for testing. The peripheral rapidly feeds a DUT to the test site, the tester tests the DUT, and the peripheral moves the DuT away from the test site, so that another DUT can be tested.
The test head and peripheral are separate pieces of machinery that generally have separate support structures. Therefore, before testing can begin it is necessary for the test head and the peripheral to be attached together. In general, this is accomplished by moving the test head toward the peripheral, carefully aligning the test head, and latching the test head to the peripheral. Once latched, a docking mechanism pulls the test head and peripheral together, causing spring-loaded contacts between the test head and peripheral to compress and form electrical connections between the tester and the DUT. This process of aligning and attaching the test head to the peripheral is commonly known as xe2x80x9cdocking.xe2x80x9d
FIG. 1 illustrates a conventional mechanism for docking a test head to a peripheral. The docking mechanism of FIG. 1 is customarily used in conjunction with the Catalyst(trademark) test system, provided by Teradyne, Inc. of Boston, Mass. As shown in FIG. 1, a docking mechanism 100 is attached to a receptacle 112. Several docking mechanisms 100 are generally attached to the outside of a test head near the top of the test head. Several receptacles are generally attached to a peripheral, in complementary locations that allow the docking mechanisms 100 to mate with the receptacles 112. The docking mechanism 100 and receptacle 112 of FIG. 1 are shown in a fully docked configuration, i.e., in the configuration they assume for electronically testing devices.
As shown in FIG. 1, the docking mechanism 100 includes a latch barrel 110 and a latchpin 118 that runs axially within the latch barrel 110. Four ball bearings 116 are positioned within holes in the latch barrel 110, around the circumference of the latchpin 118. The outer entrances to the holes are slightly deformed from perfect circles (not visible in the figure). The deformed regions form a barrier that prevents the ball bearings 116 from falling out of the latch barrel 110.
The latchpin 118 has different portions 118a and 118b along its length, and the different portions have different diameters. To effect latching and unlatching, the latchpin 118 advances and retracts with respect to the latch barrel 110. As the latchpin 118 moves, the portion of the latchpin that 118 makes contact with the ball bearings 116 changes. As a result, the radial positions of the ball bearings 116 change. For example, when the portion 118a of the latchpin with a relatively large diameter aligns with the ball bearings 116, the ball bearings extend outwardly from the center of the latch barrel 110, increasing the effective circumference of the latch barrel 110. When the portion 118b of the latchpin 118 with a relatively small diameter aligns with the ball bearings 116, the ball bearings are free to collapse inwardly, reducing the effective circumference of the latch barrel 110.
The receptacle 112 includes a washer 114 having an inner diameter just slightly larger than the outer diameter of the latch barrel 110 with the ball bearings 116 fully retracted. Depending upon the position of the latchpin 118 relative to the latch barrel 110, the ball bearings 116 either prevent the washer 114 and latch barrel 110 from separating, or allow the washer 114 to freely slide off and on the latch barrel 110.
An actuator 120 establishes the position of the latchpin 118. The latchpin 118 has a threaded portion (not visible) that extends into the actuator 120. The actuator 120 includes a nut (not visible) that has a fixed position relative to the actuator 120 and engages the threaded portion of the latchpin 118. The latchpin can be rotated under control of a motor and gears (not visible) that reside within the actuator 120. Depending upon the direction of rotation, the latchpin 118 either advances or retracts relative to the actuator 120.
FIGS. 2A-C illustrate various configurations that the docking mechanism 100 assumes during normal use. FIG. 2A shows the docking mechanism 100 in a xe2x80x9cready-to-latchxe2x80x9d configurationxe2x80x94prior to the latch barrel 110 being inserted into the receptacle 112. The latchpin 118 is fully retracted. A spring (not shown) exerts an upward force 216 on the latch barrel 110 (base region 220) relative to the latchpin 118, so that the a tab 210 extending from the latchpin 118 rests against a lower inside shoulder 214b of the latch barrel 110. The first portion 118a of the latchpin with the relatively large diameter rests against the ball bearings 116, and the ball bearings 116 partially protrude through the holes in the latch barrel 110.
FIG. 2B shows the docking mechanism 100 at the instant that the latch barrel 110 is inserted into the receptacle 112 (not shown). As the latch barrel 110 is inserted into the receptacle 112, the washer 114 catches the ball bearings 116 and exerts a downward force on them. The latch barrel 110 is then pushed downwardly, and the ball bearings 116 are moved into contact with the relatively narrow portion 118b of the latchpin 118. The ball bearings collapse inwardly, and the latch barrel 110 enters through the washer 114 of the receptacle 112. Once the ball bearings 116 clear the washer 114, the latch barrel 110 springs upwardly in response to the spring force 216. The receptacle 112 is then firmly held in place by the docking mechanism 100.
FIG. 2C shows the docking mechanism 100 in an unlatched configuration. Here, the latchpin 118 is advanced so that the tab 210 of the latchpin 118 presses against an inner upper shoulder 214a of the latch barrel 110, and the base 220 of the latch barrel 210 presses against a fixed stop 218. The fixed stop 218 has fixed position relative to the actuator 120. In this configuration, the relatively narrow portion 118b of the latchpin 118 aligns with the ball bearings 216, and the ball bearings 116 are free to collapse inwardly. The docking mechanism 100 can then be freely inserted into and withdrawn from the receptacle 112.
In addition to the configurations illustrated in FIGS. 2A-2C, the latch pin can also assume the fully docked configuration, like that shown in FIG. 1. The fully docked configuration is identical to the configuration shown in FIG. 2A, except that the latchpin 118 and latch barrel 110 are pulled down by the actuator 120. The fully docked configuration provides closer contact between the test head and the peripheral, and thus allows electrical connections to be made between the test head and the peripheral by compressing spring-loaded contacts, as described above.
Although the docking mechanism 100 has proven to be highly effective, we have recognized new requirements that make its use less attractive for certain future applications. In particular, testers have recently been developed with test heads that are significantly larger than the test head used in the Catalyst(trademark) test system. The increased size of the test head has necessitated that the docking mechanisms be relocated from the sides of the test head to top of the test head. However, the top of the test head is densely crowded with electronics and other components and cannot easily accommodate the vertical space required by the docking mechanisms 100.
In addition, a loss of power to the latching mechanism 100 causes the latching mechanism 100 to hold its position. If the test head and peripheral are docked together when a loss of power occurs, an operator must manually access the actuator 120 to undock them. In particular, the operator must rotate a shaft 122 within the actuator 120xe2x80x94generally using a crescent wrenchxe2x80x94to manually spin the gears within the actuator 120 and move the latchpin 118. If the latching mechanism is located at the top of the test head instead of at its sides, the operator would not be able to access to the shaft 122, and the test head could not be easily undocked from the peripheral.
With the foregoing background in mind, it is an object of the invention for a docking mechanism to require little vertical space compared with conventional docking mechanisms.
It is another object of the invention for a docking mechanism not to require direct access by an operator to establish an undocked condition in the event of a loss of power.
To achieve the foregoing objects and other objectives and advantages, a docking mechanism suitable for docking a test head with a peripheral includes a piston and a hollow cylindrical chamber. The piston has a first portion movably disposed within the chamber and a second portion extending from the first portion and through a hole the chamber. A latch barrel, suitable for attaching to a receptacle, extends from an opening in the second portion of the piston. A latchpin is moveably disposed within the latch barrel for establishing latching and unlatching conditions. A biasing force, provided for example by a spring, tends to bias the position of the latchpin relative to the latch barrel to the unlatched condition. By applying an active force to the latchpin, the latchpin can: be moved against the biasing force within the latch barrel for establishing the latched condition. When the active force is removed, for example upon a loss of power, the biasing force restores the latchpin to the unlatched condition. By applying fluid pressure to a surface of the piston, the piston can be moved relative to the chamber, and the extension of the latch barrel relative to the chamber can be varied.